Institution: Department of Theoretical Physics, Lund University
Postal address: Solvegatan 14A, S-223 62 LUND (Sweden)
Telephone: +46 46 2229071
Fax: +46 46 2223844
E-mail: coa@teorfys.lu.se
M. Hindgren C.-O. Almbladh
Department of Theoretical Physics, Lund University
S\"olvegatan 14 A, S-223 62 Lund (Sweden)
We study the effects of local vertex corrections to the self energy of the electron gas with and without spin-polarization. We find that a vertex derived from time-dependent density-functional theory can give accurate self energies without including the explicit time dependence of the exchange-correlation potential provided, however, that a proper decay at large momentum transfer (large $q$) is built into the vertex function. (The local-density approximation for the vertex fails badly.) Total energies are calculated from the Galitskii-Migdal formula, and it is shown that a proper large-$q$ behavior results in a close consistency between the chemical potentials derived from these energies and those obtained directly from the self energy. We show that this internal consistency depends critically on including the same vertex correction in both the self-energy and the screening function. In addition the total energies become almost as accurate as those from elaborate Monte-Carlo calculations. We also compare with total energies from variational energy functionals by Luttinger and Ward, and a recent extension by Almbladh, von Barth, This as well as previous works show that self-energy corrections are important for properly describing electron propagation at energies around and above the plasmon energy. For easy use in calculations of photoemission and x-ray extended fine structure spectra, we parametrize our calculated self-energies in terms of a simple analytical expression.
Many-body theory of excitation energies and solid state spectroscopies such as x-ray and photomeission spectra.
1. M. Hindgren and C.-O. Almbladh, Improved local-field corrections to the $G_0W$ approximation in jellium: Importance of consistency relations, Phys. Rev. B, to appear.
2. C.-O. Almbladh and M. Hindgren, Variational energy calculations: Application to the electron gas, submitted to Phys. Rev. B.
3. C.-O. Almbladh, U. von Barth, and R. van Leeuwen, New variational approach to total energies and response functions (manuscript)
Institution: Institut fuer Festkoerpertheorie und Theoretische
Optik
Postal address: Max-Wien-Platz 1, D-07743 Jena, Germany
Telephone: 0049-3641-635902
Fax: 0049-3641-635182
E-mail: bechsted@ifto.physik.uni-jena.de
WWW home page: http://www.ifto.uni-jena.de
Friedhelm Bechstedt
Friedrich-Schiller-Universitaet, Max-Wien-Platz 1, D-07743 Jena,
Germany
Actual ab initio calculations of optical properties do not need
any experimental parameter, e.g. the atomic coordinates. The density-
functional theory combined with the local-density approximation
allows the calculation of the geometrical structure of crystalline
solids and their surfaces with a precision of about one percent.
We therefore use the DFT-LDA bandstructure and single-electron
states as a reasonable starting point for the calculation of the
dielectric function within the independent-particle or random-phase
approximation. In addition, the influence of several many-body
corrections is studied. Among them are local-field effects, exchange
& correlation, quasipar- ticle shifts, and vertex corrections.
The theory is applied to group-IV semiconductors.
solution of Dyson equation for single-particle Green function
and of
Bethe-Salpeter equation for polarization function
F. Bechstedt et al., PRL 78, 1528 (1997)
V.I. Gavrilenko et al., PRB 54, 13416 (1996)
V.I. Gavrilenko et al., PRB 55, 4343 (1997)
B. Adolph et al., PRB 53, 9797 (1996)
Institution: Departement de Physique des Materiaux, UMR-CNRS 5586
Postal address: 43 bd du 11 novembre 1918, 69622 Villeurbanne,
France
Telephone: (33)04.72.44.80.00
Fax: (33)04.78.89.74.10
E-mail: xblase@dpm.univ-lyon1.fr
WWW home page: http://dpmsun1.univ-lyon1.fr/~xblase
We have developed (1), in collaboration with Prs. A. Rubio and S.G Louie, a real-space approach for the calculation of the dielectric response in extended systems. All relevant quantities (susceptibility, dielectric matrix, Coulomb potential) are calculated on a (r,r') double grid in real-space. We use auxiliary "mixed-space" fonctions, such as $\eps{\bf q}(r,r')$ (where $\bf q$ samples the Brillouin zone), which have the full periodicity of the crystal. This is of much interest when the typical "localization area" of (e.g.) $\eps(r,r')$ is much larger than the unit cell. We are presently extending this approach to quasiparticle energy calculations within the GW approximation.
(1) Blase,Rubio,Cohen,Louie, PRB {\bf 52}, R2225 (1995).
Institution: Department of Applied Physics, Eindhoven University
of Technology
Postal address: P.O. Box 512, 2500 MB Eindhoven
Telephone: +31.40.2474352
Fax: +31.40.2445253
E-mail: P.A.Bobbert@phys.tue.nl
WWW home page: http://herman.ni.phys.tue.nl/peter/
P.A. Bobbert, J.-W. van der Horst, M.A.J. Michels
Dept. of Applied Physics, Eindhoven Univ. of Tech., P.O. Box 513,
5600 MB Eindhoven, Netherlands
The electronics of conjugated polymers is both of industrial and fundamental interest. Their cheap processibility makes them ideal candidates for mass production of low-end electronic devices, such asled's, displays and plastic cards with electronic circuits. But also from afundamental point of view the electronics of these polymers is veryinteresting. There is much debate about the possible importance ofpolaronic and excitonic effects. Clearly, reliable statements are needed inthis context. Recently, the GW-quasiparticle energies of the prototype conjugated polymer poly-acetylene were calculated by Ethridge and Fry. Inthe present talk we will report on a pilot study of GW-bandstructure calculations of more complex, but industrially more relevant polymers, suchas polythiophene. Because of the large unit cell of these polymers suchcalculations require a high degree of sophistication. The space-time method of Rojas et al. is the starting point of our approach.
Ab initio electronic structure calculations. Conjugated polymers.
Institution: Universita degli Studi di Bologna, Dipartimento di
Chimica 'G. Ciamician'
Postal address: Via F. Selmi 2, I40126 Bologna, Italy
Telephone: +39.51.25.94.95
Fax: +39.51.25.94.56
E-mail: Michael@brahms.ciam.unibo.it
WWW home page:
M. S. Deleuze (a) and L.S. Cederbaum (b)
(a) c/o Pr. J. Delhalle
Laboratoire de Chimie Theorique des
Surfaces et Interfaces
FUNDP - Namur
Rue de Bruxelles, 61
B5000 Namur
Belgium
(b) Lehrstuhl fur Theoretische Chemie
Institut fur Physikalische Chemie
Universitat Heidelberg
Im Neuenheimer Feld 253
D69120 Heidelberg
Germany
Nowadays, the photoelectron spectra of thin films, microcrystals
or self-assembled layers of polymers are successfully used to
probe the molecular architecture (bonding characteristics, configuration,
conformation) at the surface (or regions near to it). Their interpretation
is most commonly conducted by comparison with quanto- mechanical
simulations based on the one-particle picture of ionization (e.g.
Koopmans' theorem). However, although not necessarily apparent
from experiment alone, the recorded structures may not relate
AT ALL to canonical one-electron states. Much more care should
be exercised for their interpretation. As demonstrated by Green's
Function calculations coping consistently with multistate configuration
interactions on model oligomers, the inner valence structures
in the ionization spectrum of polyacetylene are essentially due
to electronic correlation, whereas the outer valence region is
also substantially contaminated by shake-up lines. A severe breakdown
of the orbital picture of ionization is even found to occur for
the innermost levels of a series of alkane compounds converging
to polyethylene, a typical insulator. Besides evidences for strong
multistate interactions, this study also investigates the dependence
of shake-up bands to configurational and conformational effects,
an important question in the outlook of applications of photoionization
spectroscopy in polymer sciences.
(1) Calculation of photoionization spectra, in order to probe
molecular conformations in the gas phase, or at the surface of
polymer materials.
- M. Deleuze, J.P. Denis, J. Delhalle, B.T. Pickup,
'Theoretical Study of Spectral Differences in the XPS Valence
Bands of Poly(ethylene) Lamellae and Films',
J. Phys. Chem., 97, 5115 - 5123 (1997).
- M. Deleuze, J. Delhalle, B.T. Pickup and S. Svensson,
'Probing the Molecular Primary and Secondary Structures
of Saturated Hydrocarbons by X-ray Photoionization
Spectroscopy',
J. Am. Chem. Soc., 116, 10715 - 10724 (1994)
(2) Size-dependence aspects of Many-Body Greens' Function theory
as
applied to extended systems.
- M. Deleuze, J. Delhalle, B.T. Pickup, J.L. Calais,
'Size-Consistency and Size-Intensivity Aspects of Many-Body
Green's Function Calculations on Polymers :
Characterization of the Convergence of Direct Lattice Summations'
Adv. Quantum Chem., 26, 35 - 98 (1995).
- M. Deleuze, M.K. Scheller, L.S. Cederbaum,
'On the Size-Dependence of the Static Self-Energy in
One-particle Propagator Calculations',
J. Chem. Phys., 103, 3578 - 3588 (1995).
(3) Development of new GF schemes for the calculation of molecular
responses.
- M. Deleuze, M.J. Packer, B.T. Pickup, D.J. Wilton,
'Gauge Invariance of Linear Response Properties using the
Perturbed Electron Propagator',
J. Chem. Phys, 102, 6128 - 6144 (1995).
- M. Deleuze and B.T. Pickup,
'The Coupled Electron Propagator in the two-particle-hole (ADC2)
and extended two-particle-hole (ADC3) Tamm-Dankoff
Approximations',
Int. J. Quantum Chem., 63, 483 - 509 (1997).
(4) Calculation of the correlation bands of extended systems.
- M. Deleuze and L.S. Cederbaum,
'Formation of Satellite Bands in the Ionization Spectra of
Extended Systems',
Phys. Rev. B, 53, 13326 - 13339 (1996).
- M. Deleuze and L.S. Cederbaum,
'Evidences for a Partial Breakdown of the Molecular Orbital
Picture of Ionization in the Inner Valence Spectra of Large
Saturated Hydrocarbons',
J. Chem. Phys., 105, 7583 - 7596 (1996).
- M. Deleuze and L.S. Cederbaum,
'Correlation Effects in the X-ray Photoionization Spectra
of Ethylene, Butadiene amd Hexatriene,
Int. J. Quantum Chem., 63, 465 - 481 (1997).
(5) Structure and dynamics of giant molecules : interpretation
of their NMR and INS spectra.
- M. Deleuze, F. Zerbetto and D.A. Leigh,
'Molecular Mechanics Study of the Structure and Dynamics
of Benzylic Amide Catenanes', in preparation.
- D.A. Leigh, A. Murphy, J.P. Smart, G. Owen, M.S. Deleuze
and F. Zerbetto, 'How do Benzylic Amide Catenane Rings
Rotate ?', in preparation.
- B. Paci, M. Deleuze, R. Caciuffo, J. Tomkinson, F. Ugozzoli
and F. Zerbetto, 'Nuclear motions of an inclusion complex of
Calix(4)arene', in preparation.
On december 1st, after 3 years research as a PhD student of
Pr. J. Delhalle (FUNDP-Namur, Belgium), and three post-doctoral
stays at the universities of Sheffield (UK, Pr. B.T. Pickup),
Heidelberg (Germany, Pr. L.S. Cederbaum) and Bologna (Italy,
Dr. F. Zerbetto), M. Deleuze will take over a new position,
as a 'post-doctoraal onderzoeker voor de Fonds voor
Wetenschappelijk Onderzoek - Vlaanderen (Belgium),
at the Limburgs Universitair Centrum, Departement SBG,
B-3590 Diepenbeek, Belgium.
Institution: Dipartimento di Fisica dell'Universita' di Roma Tor
Vergata
Postal address: Via della Ricerca Scientifica n. 1 - 00133 Roma
(Italy)
Telephone: +39/6/72 59 45 22
Fax: +39/6/20 23 507
E-mail: delsole@roma2.infn.it
WWW home page: NONE
Rodolfo Del Sole, Maurizia Palummo, Massimiliano Corradini
and Giovanni Onida, Dipartimento di Fisica, Universita' di Roma
"Tor Vergata", I-00133 Roma, Italy, and
Lucia Reining, Laboratoire des Solides Irradie's, Ecole Polytechnique,
91128 Palaiseau, France.
An exchange-correlation energy functional beyond the LDA, due
to Kohn and Sham, is considered for ground state calculations
in semiconductors. An important ingredient of this functional
is the exchange-correlation kernel K_{xcj}(r;n) of the homogeneous
electron gas. When realistic forms of $K_{xcj}(r;n)$ are used,
as the one given by Ichimaru and Utsumi/1/, or our recent parametrization
of the Moroni and Senatore Quantum Monte Carlo results/2/, we
obtain small corrections to the LDA total energy of bulk Si and
C which are in agreement with Quantum Monte Carlo calculations/3/;
nevertheless, the corresponding corrections to the total energy
of the isolated atom is not large enough to yield a substantial
correction to the LDA overestimation of the cohesive energy of
the solid.
/1/ Ichimaru and K. Utsumi, Phys. Rev. B 24, 7385 (1981).
/2/ S. Moroni, D. M. Ceperley, and G. Senatore, Phys. Rev. Lett.
75, 689, (1995).
/3/ S. Fahy, X. W. Wang, and S. G. Louie, Phys. Rev. B 42, 3503
(1990).
Ab-initio calculation of the electronic structure of semiconductors
The optical properties of surfaces
Excitons
(1) L. Reining, R. Del Sole, "Quasi one-dimensional excitons
and the
optical properties of Si(111)2x1", Phys. Rev. Lett. 67, 3816
(1991).
(2) R. Del Sole, L.Reining and R.W. Godby, "GWG approximation
for electron self-
energy in semiconductors and insulators", Phys. Rev. B 49,
8024 (1994).
(3) G. Onida, L. Reining, R. W. Godby, R. Del Sole, W. Andreoni,
"Ab initio
calculations of the quasiparticle and absorption spectra of clusters:
the sodium tetramer", Phys. Rev. Lett. 75, 818 (1995).
(4) R.Del Sole, "Reflectance spectroscopy - theory"
in "Photonic probes of
surfaces" edited by P.Halevi (Elsevier, Amsterdam, 1995);
pag. 131
Institution: MPI for Physics of Complex Systems
Postal address: Nöthnitzer Str. 38, D-01187 Dresden
Telephone: +49-351-871-1101
Fax: +49-351-871-1199
E-mail: schuppe@mpipks-dresden.mpg.de
WWW home page:
P. Fulde
Max-Planck-Institut für Physik komplexer Systeme,
Nöthnitzer Straße. 38,
D-01187 Dresden (Germany)
We present a method for calculating the valence bands of covalent semiconductors which uses information from quantum-chemical {\sl ab initio} calculations on appropriate molecules. From those calculations local matrix elements are extracted which enter an incremental expansion of the bulk band structure. A comparison with the results of other methods is made. Present work is described which extends our computational scheme to conduction bands.
Our work on electronic excited states in solids has been proceeding along three different lines:
\item energy bands of group-IV semiconductors:here we start from a SCF band structure calculation using CRYSTAL andinclude correlation effects by employing quantum chemical methods implemented in the ab initio program package MOLPRO together with anincremental technique
\item spectral densities of strongly correlated electron systems: calculations are done by using multiband Hubbard Hamiltonians and employing Green's function methods based on projectiontechniques as well as approximate solutions of Faddeev type of equations (applications: $Ni, NiO, Cu-O$ planes)
\item low-energy excitations in heavy-fermion systems:renormalized band structure calculations are done in order to computethe huge mass anisotropies in materials like $Ce Ru_2Si_2$
References:
J. Gr\"afenstein, H. Stoll and P. Fulde, Phys. Rev. B {\bf 55},13588 (1997)
P. Fulde, ''Electron Correlations in Molecules and Solids'' 3rd ed. (Springer, Berlin, Heidelberg, 1995)
J. Igarashi, P. Unger, K. Hirai and P. Fulde, Phys. Rev. B {\bf49}, 16181 (1994)
P. Unger, J. Igarashi and P. Fulde, Phys. Rev. B {\bf 50}, 10485(1994)
G. Zwicknagl, Adv. Phys. {\bf 41}, 203 (1993)
Institution: Department of Physics, University of York
Postal Address: York YO1 5DD, U.K.
Telephone: +44 1904 432231
Fax: +44 1904 432214
E-mail: rwg3@york.ac.uk
WWW home page: http://www-users.york.ac.uk/~rwg3/
M.M. Rieger**, L. Steinbeck*, A. Schindlmayr**, T. Pollehn**,
R.W. Godby* and R.J. Needs**
*Department of Physics, University of York, York YO1 5DD, U.K.
**Cavendish Laboratory, University of Cambridge, Cambridge CB3
0HE, U.K.
We present an efficient space-time method [1] for performing first-principles calculations of the Green's function of many-body theory and associated quantities. The most important part of this method computationally is the calculation of the key quantities in real space and imaginary time. This procedure makes use of the fact that there is markedly less structure along the imaginary axis than along the real axis in both the time and energy complex planes, although full information is retained. The dynamic screening of the Coulomb interaction (at the RPA level) is represented arbitrarily accurately, without any need for the introduction of model energy-dependence. We present the results of calculations of the full self-energies, spectral functions and charge densities of jellium, silicon, and larger unit cells.
We also discuss the inclusion of vertex corrections beyond the GW approximation, for investigations of materials in which correlation is stronger. Previous [2] and current work on Hubbard systems is being used to guide the ab initio calculations.
[1] H.N. Rojas, R.W. Godby and R.J. Needs, Phys. Rev. Lett. 74 1827 (1995)
[2] C. Verdozzi, R.W. Godby and S. Holloway, Phys. Rev. Lett. 74 2327 (1995)
Ab initio many-body perturbation theory
"Evaluation of GW approximations for the self-energy of a Hubbard cluster", C. Verdozzi, R.W. Godby and S. Holloway, Phys. Rev. Lett. 74 2327 (1995). Abstract
"Space-time method for ab initio calculations of self-energies and dielectric response functions of solids", H.N. Rojas, R.W. Godby and R.J. Needs, Phys. Rev. Lett. 74 1827 (1995). Abstract
"Ab initio calculations of the quasiparticle and absorption spectra of clusters: the sodium tetrameter", G. Onida, L. Reining, R.W. Godby, R. Del Sole and W. Andreoni, Phys. Rev. Lett. 75 818 (1995). Abstract
"Elimination of unoccupied state summations in ab initio self-energy calculations for large supercells", L. Reining, G. Onida and R.W. Godby, accepted for publication in Physical Review B (Rapid Communications) (1997). Abstract
"Assessment of Many-Body Approximations using Hubbard Chains", Thomas Pollehn, Arno Schindlmayr and R.W.Godby, submitted. Abstract
Fundamentals of density-functional theory
"Density-polarisation functional theory of the response of a periodic insulating solid to an electric field", X. Gonze, P. Ghosez and R.W. Godby, Phys. Rev. Lett. 74 4035 (1995). Abstract LaTeX or PostScript from LANL e-print server
"Density-functional theory of polar insulators", X. Gonze, Ph. Ghosez and R.W. Godby, Phys. Rev. Lett. 78, 294 (1997) Abstract LaTeX or PostScript from LANL e-print server
"Polarization-Dependence of the Exchange Energy", X. Gonze, Ph. Ghosez and R.W. Godby, Phys. Rev. Lett. 78 2029 (1997). Abstract
"The long-wavelength behaviour of the exchange-correlation
kernel in the Kohn-Sham theory of periodic systems", Ph.
Ghosez, X. Gonze and R.W. Godby, to appear in Phys Rev. B (1997).
Abstract
LaTeX or PostScript from LANL e-print server
Institution: Institut für Theoretische Physik, Universität
Würzburg
Postal address: Am Hubland, D-97074 Würzburg, Germany
Telephone: ++49-931-888-5724
Fax: ++49-931-888-5141
E-mail: gross@physik.uni-wuerzburg.de
E.K.U. Gross
Institut für Theoretische Physik, Universität Würzburg
A density functional formalism comparable to the theory of Hohenberg, Kohn and Sham is developed for interacting many-body systems subject to time-dependent electric [1] and magnetic [2] fields. The formalism leads to a set of time-dependent Kohn-Sham equations which in addition to the external potential contain a time-dependent Hartree term and a time-dependent exchange-correlation potential. To obtain approximations of the latter, an extension of the so-called optimized potential method into the time-dependent domain is presented [3]. Applications of the formalism within and beyond the linear-response regime will be discussed.
Within the regime of linear response theory, the time-dependent Kohn-Sham equations lead to a formally exact representation of the frequency-dependent linear density response [4]. Since the latter has poles at the true (correlated) excitation energies, the formalism can be used for the calculation of excitation energies. A simple additive correction to the Kohn-Sham orbital-energy differences will be deduced and results for atomic and molecular singlet and triplet excitation energies [4,5] will be presented. For high-lying excitations the quantum defect is investigated.
Beyond the regime of linear response, time-dependent density-functional theory is employed to describe atoms in strong femtosecond laser pulses. All-electron calculations have been performed for helium and neon. Ionization yields and harmonic spectra will be presented and compared with experimental data. A systematic study of harmonic generation in two-color lasers is performed for the helium atom. [6]
[1] E. Runge, E.K.U. Gross, Phys. Rev. Lett. 52, 997 (1984).
[2] O.-J. Wacker, R. Kümmel, E.K.U. Gross, Phys. Rev. Lett. 73, 2915 (1994).
[3] C.A. Ullrich, U.J. Gossmann, E.K.U. Gross, Phys. Rev. Lett. 74, 872 (1995).
[4] M. Petersilka, U.J. Gossmann, E.K.U. Gross, Phys. Rev. Lett. 76, 1212 (1996).
[5] M. Petersilka, E.K.U. Gross, Int. J. Quant. Chem. Symp. 30, 1393 (1996).
[6] S. Erhard, E.K.U. Gross, in: "Multiphoton Processes", edited by P. Lambropoulos and H. Walther, Institute of Physics (1996), p. 37 - 46.
1. Time-dependent density functional theory. Review article: E.K.U. Gross, J.F. Dobson, M. Petersilka, in: "Density Functional Theory", edited by R.F. Nalewajski, Springer series 'Topics in Current Chemistry', vol. 181 (1996), p. 81 - 172
2. Current-density functional theory of systems in strong magnetic fields:
K. Capelle, E.K.U. Gross, Phys. Rev. Lett. 78, 1872 (1997)
S. Erhard, E.K.U. Gross, Phys. Rev. A 53, R5 (1996)
3. Superconductivity:
K. Capelle, E.K.U. Gross, B.L. Gyorffy, Phys. Rev. Lett. 78, 3753 (1997)
K. Capelle, E.K.U. Gross, Phys. Lett. A 198, 261 (1995)
L.N. Oliveira, E.K.U. Gross, W. Kohn, Phys. Rev. Lett. 60, 2430 (1988)
4. Orbital functionals in DFT, optimized-potential method:
T. Grabo, E.K.U. Gross, Int. J. Quant. Chem. 64, 95 (1997)
T. Grabo, E.K.U. Gross, Chem. Phys. Lett. 240, 141 (1995)
Institution: Max-Planck Institut
Postal address: Postfach 800 665, D-70506 Stuttgart
Telephone: xx49-711-6891669
Fax: xx49-711-6891010
E-mail: gunnar@and.mpi-stuttgart.mpg.de
WWW home page: http://librix.mpi-stuttgart.mpg.de/docs/ANDERSEN/
Olle Gunnarsson
Max-Planck-Institut für Festkörperforschung, Stuttgart
The alkali-doped fullerenes are interesting systems, being strongly correlated and being superconductors with a relatively high Tc. Due to the large number of atoms in the unit cell and the importance of correlation, it is hard to perform reliable ab initio calculations for these systems. It is discussed how to construct a realisitic model Hamiltonian and how to determine its parameters. The model Hamiltonian is then treated in a projection T=0 Quantum Monte Carlo method for obtaining ground-state properties and within a diagramatic approach for obtaining some excited state properties.
Fullerenes, transition metal oxides, Ce compounds, Quantum Monte Carlo methods, GW (lowest order self-energy in screened interaction) approximation, exact diagonalization methods
O. Gunnarsson, E. Koch and R.M. Martin: Mott Transition in Degnerate Hubbard Models: Application to Doped Fullerenes, Physical Review B 54, R11026 (1996) URL.
O. Gunnarsson: Superconductivity in Fullerides, Rev. Mod. Phys. 69, 575 (1997) URL
O. Gunnarsson: Hubbard model with orbital degeneracy and integer or noninteger filling, Z. Phys. B (in press) URL
O. Gunnarsson and E. Koch: Discrete Hubbard-Stratonovich transformations for systems with orbital degeneracy URL
Institution: MPI-FKF
Postal address: Heisenbergstrasse 1, D-70569 Stuttgart, Germany
Telephone: +49-711-689 1593
Fax: +49-711-689 1595
E-mail: hedin@audrey.mpi-stuttgart.mpg.de
WWW home page: http://www/docs/frames.html
John Michiels(1), Lars Hedin(1) and John Inglesfield(2)
(1) MPI-FKF, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
(2) Univ of Wales, College of Cardiff, PO Box 913, Cardiff CF2
3YB, GB
We compare different approximations to calculate core electron
photoemission, trying to understand the transition from the adiabatic
to the sudden limits. We study a model case of an atom embedded
in a semi-infinite jellium. At low photoelectron energies we use
the Inglesfield-Bardyszewski-Hedin quantum-mechanical approximation
(QM), at somewhat higher energies a semi-classical approach with
quantum-mechanically calculated loss from a photoelectron moving
on a trajectory (SC), and at high energies the Spicer three-step
model (TRANSP). Comparisons are also made with the Tougaard approach.
SC agrees quite well with QM already at say twice the plasmon
energy above threshold, while TRANSP does not agree until the
order of tenths of plasmons energies. The approach to the sudden
limit is illustrated by a curve over the integrated intensity
of the satellites relative to that of the main peak as a function
of photo-electron energy. For energies when the satellite electrons
have an energy below the plasmon threshold while the primary electron
has an energy above, this curve has a pronounced peak due to the
comparatively long mean free part of the electrons in the satellite.
As models for the dielectric function of the semi-infinite jellium,
we use the Inglesfield and the Bechstedt coupling functions, as
well as the RPA infinite-barrier function. The latter includes
interference between the incoming and reflected electrons. We
derive a general expression for the relation between an RPA-type
dielectric function and the fluctuation potential needed in the
QM approach. The Inglesfield, Bechstedt and RPA fluctuation potentials
show only minor differences, except at very low energies.
Ref. Bardyszewski W and Hedin L, 1985, Physica Scripta 32, 439-50
A new approach to the theory of photoemission in solids
Many-body theory of elctron correlation. Bandstructure.
Spectroscopies like photoemission, x-ray absorption and electron
scattering.
Bardyszewski W and Hedin L, 1985, Physica Scripta 32, 439-50
A new approach to the theory of photoemission in solids
Fujikawa T, Hedin L, 1989, Phys Rev B 40, 11 507-18
Theory of electron scattering from solids
Hedin L, 1991, Nucl Instr and Methods in Physics Research A 308,169-177
(1991)
Properties of electron self-energies and their role in electron
spectroscopies
Hedin L, 1995, IJQC 56, 445-52
Electron correlation:Keeping close to an orbital description
Aryasetiawan F, Hedin L, Karlsson K, 1996, PRL 77, 2268
Multiple plasmon satellites in Na and Al spectral functions from
ab initio cumulant expansion
Institution: University Of California at Berkeley
Postal Address: Department of Physics, University of California,
Berkeley, CA 94720, USA
Telephone: 510-642-1709
Fax: 510-643-9473
E-mail: louie@jungle.berkeley.edu
WWW home page: http://tiger.berkeley.edu/louie
Steven G. Louie
Department of Physics, University of California at Berkeley, Berkeley,
CA
94720 and Materials Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, CA 94720.
The quasiparticle energies and optical spectra of small clusters
are calculated using ab initio Green's-function-based and quantum
Monte Carlo techniques. The effects of self energy corrections
and electron-hole interactions in the excitation energies of a
series of small Si clusters capped with hydrogen are examined.
Results are compared to available experimental data and to results
obtained using other theoretical methods.
My research interests are in theoretical condensed matter physics including: the electronic and structural properties of solids, surfaces, interfaces and clusters; quasiparticle excitations in solids; electron correlation effects in bulk and reduced dimensional systems; materials under high pressure; fullerenes and nanotubes; structural phase transitions; and ab initio pseudopotential theory.
Some papers relevant to the Workshop:
1. M. S. Hybertsen and S. G. Louie, "First Principles Theory of Quasiparticles: Calculation of Band Gaps in Semiconductors and Insulators," Phys. Rev. Lett. 55, 1418 (1985). M. S. Hybertsen and S. G. Louie, "Electron Correlation in Semiconductors and Insulators: Band Gaps and Quasiparticle Energies," Phys. Rev. B 34, 5390 (1986).
2. M. S. Hybertsen and S. G. Louie, "Theory of Quasiparticle Surface States in Semiconductor Surfaces," Phys. Rev. B 38, 4033 (1988).
3. E. Shirley, X. Zhu, and S. G. Louie, "Core-Polarization in Semiconductors: Effects on Quasiparticle Energies," Phys. Rev. Lett. 69, 2955 (1992).
4. X. Blase, A. Rubio, S.G. Louie, and M.L. Cohen, "A Mixed-Space Formalism for the Dielectric Response in Periodic Systems," Phys. Rev. B 52, R 2225 (1995).
5. S.G. Louie, "Quasiparticle Theory of Electron Excitations in Solids," in Quantum Theory of Real Materials, eds. J.R. Chelikowsky and S.G. Louie, (Kluwer Press, Boston, 1996), p. 83.
For more information see: http://tiger.berkeley.edu/louie
Institution: IRRMA
Postal address: PPH Ecublens, 1015 Lausanne, Switzerland
Telephone: 0041-21-6935428
Fax: 0041-21-6936655
E-mail: mauri@irrma.epfl.ch
excitonic self-trapping:
F. Mauri and R. Car First-principles study of excitonic self-trapping in diamond Phys. Rev. Lett. 75, 3166 (1995)
dielectric linear and non-linear susceptibility:
Dal Corso, F. Mauri and A. Rubio Density-functional theory of the nonlinear optical susceptibility: application to cubic semiconductor Phys. Rev. B 53, 15638 (1996).
A. Dal Corso and F. Mauri Wannier and Bloch orbital computation of the nonlinear susceptibility Phys. Rev. B 50, 5756 (1994) (Rapid Communications).
Institution: University of Cambridge
Postal address: TCM Group, Cavendish Laboratory, Madingley Road,
Cambridge CB3 0HE, United Kingdom
Telephone: 44 1223 337384
Fax: 44 1223 337356
E-mail: rn11@phy.cam.ac.uk
WWW home page: _
R.J. Needs, A.J. Williamson, P.R.C. Kent, Randolph Q. Hood, and
G. Rajagopal
TCM Group, Cavendish Laboratory, Madingley Road, Cambridge CB3
0HE, United Kingdom
Quantum Monte Carlo techniques are normally used to calculate
ground state properties, although they are also able to address
excited state problems. In this talk I will discuss different
ways of calculating excited state energies of solids using variational
and diffusion quantum Monte Carlo (VMC and DMC) techniques, giving
results for silicon to illustrate the methods. The first method
is a direct calculation of excited state energies of the N-electron
system using the fixed-node DMC method. Correlated guiding wave
functions are formed by replacing a ground state orbital in the
determinantal part of the wave function by an excited state orbital.
The quality of the results is controlled by the accuracy of the
nodal surface of the excited state guiding wave functions. We
also present the results of DMC calculations of the ground state
energies of the N, N+1, and N-1 electron systems, from which we
obtain the band gaps at different points in the Brillouin zone.
Finally, VMC calculations of excitation energies will be presented
using a "Generalized Koopmans' Theorem" approach.
Electronic structure calculations for condensed matter.
Density functional methods.
Quantum Monte Carlo methods.
"Quantum Monte Carlo calculations for solids using special
k-points
methods", G. Rajagopal, R.J. Needs, S. Kenny, W.M.C. Foulkes,
and
A. James, Phys. Rev. Lett. 73, 1959 (1994).
"Quantum Monte Carlo investigation of exchange and correlation
in
silicon", R.Q. Hood, M.-Y. Chou, A.J. Williamson, G. Rajagopal,
R.J. Needs, and W.M.C. Foulkes, Phys. Rev. Lett. 78, 3350 (1997).
"Diffusion quantum Monte Carlo calculations of the band structure
of
silicon", A.J. Williamson, R.Q. Hood, R.J. Needs, and G.
Rajagopal,
submitted to Phys. Rev. Lett.
Institution: Dipartimento di Fisica dell'Universita' di Roma Tor
Vergata
Postal address: Via della Ricerca Scientifica n. 1 - 00133 Roma
(Italy)
Telephone: +39/6/72 59 45 23
Fax: +39/6/20 23 507
E-mail: onida@roma2.infn.it
WWW home page: NONE
Giovanni Onida, Rodolfo del Sole and Olivia Pulci, Dipartimento di Fisica, Universita' di Roma "Tor Vergata", I-00133 Roma, Italy, and
Lucia Reining, Laboratoire des Solides Irradie's, Ecole Polytechnique, 91128 Palaiseau, France.
We present a first-principles calculation of the electronic structure and Reflection Anisotropy Spectrum for the (110) Gallium Arsenide surface. We work in the independent-quasiparticle scheme, obtaining the electronic bandstructure within Green's function theory, using the Hedin's GW approach for the self-energy operator.
In this scheme, DFT-LDA results can be used as the starting point, in a first-order perturbative approach /1/.
Three main results are obtained:
a:) the self--energy shifts with respect to LDA are larger for valence surface--localized states than for bulk states, at odd with the commonly assumed ``scissor operator'' (rigid shift) hypothesis; This effect was predicted in a previous paper by Bechstedt and Del Sole /2/.
b:) an extrapolation of the results to more bands and k--points is nevertheless still possible, since the computed shifts display an almost linear dependence on the surface localization of the wavefunction: this allows us to realize a well--converged calculation of the optical properties based on the GW--corrected spectrum;
c:) the agreement with experimental data is improved with respect to LDA level calculations.
References:
/1/ R.W. Godby, M. Schluter, L.J. Sham, Phys. Rev. B 37, 1059 (1988).
/2/ F. Bechstedt and R. Del Sole, Solid State Commun. 74, 41 (1990).
- First-Principles calculations of surface optical properties:
calculation of reflectance Anisotropy Spectra and Differential
Reflectivity Spectra of semiconductors, within LDA and beyond
(refs.1,2)
- Development of technical improvements in order to extend ab
initio self-energy calculations to more complex systems: we work
on methods to avoid the summation over, and hence the calculation
of, the empty states appearing in the expressions of response
functions
which make use of spectral representations. (refs.3,4)
- Ab initio calculations of electronic spectra in clusters (ref.3).
- Ab initio calculation of excitonic effects (ref.5)
- Developement of non-local density approximations for the density
functional theory (ref.6)
References:
(1) O.Pulci, G.Onida, A. I. Shkrebtii, R. Del Sole, B. Adolph,
"Plane-wave pseudopotential calculation of the optical properties
of GaAs", Phys. Rev. B 55, 6685 (1997).
(2) O.Pulci, G.Onida, C. Kress, A.Shkrebtii, R.Del Sole "Surface
optical properties from first principles calculations: GaAs(110),
Si(100)2x1, C(100)2x1" Proc. of 23rd Int. conf. on the physycs
of Semicond. (ICPS23), p.815, Berlin, World Scientific, 1996.
(3) G. Onida, L. Reining, R. W. Godby, R. Del Sole, W. Andreoni,
"Ab initio calculations of the quasiparticle and absorption
spectra of clusters: the sodium tetramer", Phys. Rev. Lett.
75, 818 (1995).
(4) L. Reining, G. Onida, and R. W. Godby, "Elimination of
unoccupied states summations in ab initio self-energy calculations
for large supercells", to appear Phys. Rev. B Rapid Comm.
(15 august 1997)
(5) S. Albrecht, G.Onida, L. Reining "Ab initio calculation
of quasiparticle spectrum and excitonic effects in Li2O",
Phys. Rev. B 55, 10278 (1997).
(6) M. Palummo, G. Onida, R. Del Sole, and L. Reining, "Electronic
structure calculations beyond the local density approximation:
application to silicon", Proceedings of the 23rd international
conference on The Physics of Semiconductors (ICPS 23) p. 609,
Berlin, World Scientific, 1996.
Institution: Kansas State University
Postal address: Department of Chemistry, Kansas State University,
111 Willard Hall, Manhattan KS 66506-3701, U.S.A.
Telephone: 785-532-6071
Fax: 785-532-6666
E-mail: ortiz@nestor.chem.ksu.edu
WWW home page: http://www.ksu.edu/chem/faculty/Ortiz/group.html
by J.V. Ortiz, Department of Chemistry, Kansas State University, Manhattan KS 66506-3701, U.S.A.
Electron propagator methods are now among the most powerful tools for calculating electron binding energies of molecules. New approximations based on superoperator theory and alternative choices for reference states have been implemented with parallelized, semidirect algorithms in program suites that are generally available to computational chemists. Calculations on photoelectron spectra of large molecules such as polycyclic aromatic hydrocarbons, carbon clusters and DNA bases are useful in assigning final states. Optimizations on potential energy surfaces are founded on size-extensive reference state energies derived from contour integrals and on analytical gradients of propagator poles. These techniques have been useful in determining adiabatic electron binding energies, especially where symmetry dilemmas have complicated calculations employing variational techniques. The flexibility of the propagator formalism in choosing reference states has been exploited in studies of core ionization energies and in the treatment of molecules with partial open-shell character. Because electron propagator theory provides a one-electron picture of chemical bonding that systematically treats electron correlation, it serves as a bridge between rigorous, ab initio theory and the qualitative molecular orbital concepts that inform contemporary chemical intuition. Studies on polysilanes, polyphosphazanes and metal-carbon clusters illustrate electron propagator theory's ability to extract qualitative lessons from quantitatively accurate calculations.
http://www.ksu.edu/chem/faculty/Ortiz/group.html
J.V. Ortiz, The Electron Propagator Picture of Molecular Electronic
Structure, in Computational Chemistry: Reviews of Current Trends,
Vol.
2, J. Leszczynski, ed., World Scientific, Singapore, 1997.
J.V. Ortiz, V.G. Zakrzewski and O. Dolgounitcheva, One-Electron
Pictures of Electronic Structure: Propagator Calculations on
Photoelectron Spectra of Aromatic Molecules, in Conceptual Trends
in
Quantum Chemistry, Vol. 3, E.S. Kryachko, ed., Kluwer, Dordrecht,
in
press.
Electron propagator theory provides a framework for the systematic inclusion of electron correlation in a one--electron picture of molecular electronic structure. Propagator calculations produce Dyson orbitals and correlated electron binding energies without determining wavefunctions and energies of individual states. Several approximate propagators are accurate and efficient tools for the computation of vertical and adiabatic electron binding energies. The association of Dyson orbitals to electron binding energies facilitates interpretation of electronic structure in terms of one--electron concepts.
J.V. Ortiz, Calculation and Interpretation of Total Energies in
Electron Propagator Theory, J. Chem. Phys. 103 (1995) 5630.
V.G. Zakrzewski, J.V. Ortiz, J.A. Nichols, D. Heryadi, D.L. Yeager
and
J.T. Golab, Comparison of Perturbative and Multiconfigurational
Electron Propagator Methods, Int. J. Quant. Chem. 60 (1996) 29.
J.V. Ortiz, The Electron Propagator Picture of Molecular Electronic
Structure, in Computational Chemistry: Reviews of Current Trends,
Vol.
2, J. Leszczynski, ed., World Scientific, Singapore, 1997.
J.V. Ortiz, V.G. Zakrzewski and O. Dolgounitcheva, One-Electron
Pictures of Electronic Structure: Propagator Calculations on
Photoelectron Spectra of Aromatic Molecules, in Conceptual Trends
in
Quantum Chemistry, Vol. 3, E.S. Kryachko, ed., Kluwer, Dordrecht,
in
press.
http://www.ksu.edu/chem/faculty/Ortiz/group.html
Institution: Trinity College Dublin
Postal Address: Department Of Physics, Dublin 2
Telephone: +353-1-608-1468
Fax: +353-1-671-1759
E-mail: Charles.Patterson@tcd.ie
WWW home page: http://www.tcd.ie
Optical properties of semiconductors (surfaces and highly excited
bulk
semiconductors)
Institution: University of Sheffield
Postal address: Department of Chemistry, University of Sheffield,
Sheffield S3 7HF, UK
Telephone: +114 222 9530
Fax: +114 273 8673
E-mail: B.T.Pickup@sheffield.ac.uk
M.S. Deleuze, B.T. Pickup and D.J. Wilton Department of Chemistry University of Sheffield, Sheffield S3 7HF, UK
The electron propagator for a pure ground electronic state contains information about electron ionisation and attchment processes. This talk shows how perturbation theory can be used to develop the theory of the propagator in the presence of an external applied field [1,2]. Hence, we shall show how the first order electron propagator can be used to derive static linear response properties (polarizabilities and susceptibilities) [3,4]. An interchange theorem ensures that only the first order perturbed density is needed to obtain a formula for quadratic response tensors.
[1] "The perturbed electron propagator approach to molecular response properties", B.T. Pickup, Int. J. Quantum Chem. Symp., 26, 13-30 (1992).
[2] "Along the Coulson Contour", (B.T. Pickup), (Proceedings of the Conference on Density Functional Theory and its Applications, Jesus College, Oxford, 16-18 September 1992), Phil. Mag., 69, 799-805, (1994).
[3] "Gauge Invariance of Linear Response Properties using the Coupled Perturbed Electron Propagator", (M.S. Deleuze and B.T. Pickup), J. chem. Phys., 102, 6128-6144 (1995).
[4] "The Coupled Perturbed Electron Propagator in the two-particle-hole and extended two-particle-hole approximations", (M. Deleuze and B.T. Pickup), Int J. Quantum Chem. 63, 483-509 (1997).
My research interests in the Green's function area tend to have specialised on the one-electron propagator and its relevance to the understanding of molecular photoionisation processes, particularly in the area of photelectron spectroscopy [2]. I was jointly responsible for the superoperator approach to the computation of the electon propagator [1]. This alternative to diagrammatic approaches has been widely used in quantum chemistry over the last 25 years. More recently I have been interested in the theory of ionization processes in polymers [3,4] and particularly in the use of Green's function methods to allow the elucidation of molecular conformation of extended systems at surfaces.
[1] "Direct calculations of ionisation energies I Closed shell molecules." (B. T. Pickup and O. Goscinski), Mol. Phys., 26, (1973), 1013-35.
[2] "Plane wave and orthogonalized plane wave many body Green's function calculations of photoionisation intensities", (M. Deleuze, B.T. Pickup, and J. Delhalle), Molec. Phys., 83, 655-686 (1994).
[3] "The Size Extensivity and Size Consistency of an Analysis of Linear Response Properties using the Perturbed Electron Propagator", (M.S. Deleuze and B.T. Pickup), J. chem. Phys., 102, 8967-8977 (1995).
[4] "Size-consistency and size-intensivity aspects of Many-Body
Green's function calculations on polymers: characterisation of
the convergence of direct lattice self-energy summations",
M.Deleuze, J. Delhalle, B.T. Pickup, and J-L. Calais, Advan. Quantum
Chem., 26, 35-98 (1995).
Institution: Laboratoire Des Solides Irradies, Ecole Polytechnique
Postal address: 91128 Palaiseau, France
Telephone: 0033-1-69333690
Fax: 0033-1-69333022
E-mail: REINING@MONET.POLYTECHNIQUE.FR
WWW home page: NONE
Stefan Albrecht and Lucia Reining, Laboratoire des Solides Irradiés,
Ecole Polytechnique, 91128 Palaiseau, France, and
Giovanni Onida and Rodolfo Del Sole, Dipartimento di Fisica,
Universita' di Roma "Tor Vergata", I-00133 Roma, Italy
Ab initio calculations, based on the Density Functional Theory (DFT) in the Local Density Approximation (LDA), allow for the description of the ground state properties of a wide class of materials. Also one-quasiparticle excitations can be obtained with good precision by adding self-energy corrections to the DFT-LDA eigenvalues. A realistic description of two-particle excitations, like the creation of electron-hole pairs in absorption experiments, is hardly feasible for systems where the electron and the hole interact. In this work we show how such excitonic effects can be included in ab initio electronic structure calculations, via the solution of an effective two-particle equation. Results for different systems are presented.
(1) Ab initio calculation of excitonic effects (see abstract)/1 - 3/
(2) Development of technical improvements in order to extend ab initio self-energy calculations to more complex systems. In particular, we work on methods to avoid the summation over, and hence the calculation of, the empty states appearing in the expressions of response functions which make use of spectral representations. /4/
(3) Ab initio calculations of electronic spectra in clusters. /1/ One - and two- particle excitations in small clusters are calculated. This includes technical developments, i.e. of codes which are particularly appropriate for the treatment of finite systems, and the inclusion of physical ingredients which are important in such systems: structural relaxations, electron-hole interaction.
/1/ G. Onida, L. Reining, R. W. Godby, R. Del Sole, and W. Andreoni,
Phys. Rev. Lett. 75, 818 (1995)
/2/ S. Albrecht, G. Onida, and L. Reining, Phys. Rev. B 55, 10278
(1997) /3/ S. Albrecht, G. Onida, L. Reining, and R. Del Sole,
"Ab initio calculation of excitonic effects in realistic
materials", to appear Proceedings ICAM'97/E-MRS'97 Spring
Meeting, Strasbourg, Computational Materials Science (1997)
/4/ L. Reining, G. Onida, and R. W. Godby, "Elimination of
unoccupied states summations in ab initio self-energy calculations
for large supercells", to appear Phys. Rev. B Rapid Comm.
(15 august 1997)
Institution: Dipartimento di Fisica Teorica, Universita` di Trieste
Postal address: Strada Costiera 11, 34014 Trieste, Italy
Telephone: +39-40-2240264
Fax: +39-40-224601
E-mail: resta@axpts1.ts.infn.it
WWW home page: http://ale2ts.ts.infn.it:6163/~resta/plan.txt
At a very early time, I was interested in GF calculations in molecules [R. Moccia, R. Resta, and M. Zandomeneghi, Chem. Phys. Lett. 37, 556 (1976)]. More recently, I got involved in simplified GW calculations in solids [S. Massidda, R. Resta, M. Posternak, and A. Baldereschi, Phys. Rev. B 52, 16977 (1995)]. I also have some interests in the fundaments of DFT [R. Resta, Phys. Rev. Lett. 77, 2265 (1996)]. The core of my research interests is in phenomena concerning dielectric polarization [R. Resta, Rev. Mod. Phys. 66, 899 (1994); Europhysics News 28, 18 (1997)].
Institution: Departamento Fisica Teorica. University of Valladolid
Postal address: C/ Prado de la Magdalena s/n
Telephone: ++34-83-423263
Fax: ++34-83-423013
E-mail: arubio@mileto.fam.cie.uva.es
WWW home page: http://www.fam.cie.uva.es/~arubio
Angel Rubio ( Departamento de F\'{\i}sica Te\'orica, Universidad
de
Valladolid, E-47011 Valladolid, Spain)
Llorenc Serra (Departament de Fisica, Universitat de les Illes
Balears,
E-07071 Palma de Mallorca, Spain )
We present a generalized time-dependent density-functional-theory (TDDFT)for the optical response of metal clusters where bothcore polarization and valence responses are treated microscopically. It is shown that the valence electrons response is described by an effective external field and residual interaction that are those of the standard TDDFT modified by the selfconsistent contributions of the array of polarizable ionic cores.As an application the equations are solved within the adiabatic local-density-approximation for silver clusters,where core $4d$ electrons greatly influence the optical response. Theexperimental data is well reproduced by the present theory.- Article published in Physical Review Letters 78, 1428-1431 (1997)
The main areas of research in our group are:
- Optical properties of nanostructires: metallic and semiconductor
cluster.
Absorption, qusiparticles, electron emission, etc..
- Electronic and structural properties of nanotubes: Carbon and
composite
nanotubes (BCN). Molecular dynamics simulations using ab-initio
and
empirical and semiempirical models. Fullerenes.
- Path-integral simulations.
- Density functional theory: formalism, development of non-local
functionals
and time-dependent models.
Institution: Department of Chemystry, University of Perugia
Postal address: Via Elce di Sotto, 8 - 06123 Perugia - Italy
Telephone: +39-75-5855516
Fax: +39-75-5855606
E-mail: sgam@thch.unipg.it
WWW home page:
A. Sgamellotti, F. Tarantelli
Dipartimento di Chimica, Universita' di Perugia, I-06123 Perugia,
Italy
L.S. Cederbaum
Theoretische Chemie, Universitat Heidelberg, D-6900 Heidelberg,
Germany
The study of molecular doubly ionized states is a subject of wide and rapidly growing interest. Valuable information on the electronic structure of molecules and atoms in different chemical environments can be extracted from such investigations, for which a variety of experimental techniques, based on different processes of formation of the dications, are today available. Among these, Auger spectroscopy is the most widely used. Molecular double ionization spectra are generally characterized by the fact that a very large number of dicationic states is experimentally observable and the high density of electronic states is invariably accompained by substantial electron correlation effects.
The two-particle Green's function theory, with particular focus on the Algebraic Diagrammatic Construction (ADC) formalism, is reviewed. The most advantageous feature of the Green's function approach is that it provides a framework for the direct calculation of the whole ionization spectrum (ionization energies and spectroscopic amplitudes), without resorting to the calculation of the wave-function and energy of each individual final state. A number of applications of the second order ADC(2) scheme is discussed in order to demonstrate the efficacy of this Green's function approach in the calculation and interpretation of Auger spectra of relatively large molecules.
To gain insight into the nature and properties of the very many dicationic states that can thus be computed, a key step is the analysis of their spatial charge distribution. This can made quantitative through a population analysis of the two-hole density, providing essential information on the extent of hole localization phenomena which, in addition, can be qualitatively related to the Auger intensity distribution. To be able to estimate the main features of this distribution is of key importance for the simulation of dense Auger spectra of polyatomics, where it would be prohibitive and statistically unnecessary to compute ab-initio individual state intensities. This report intends to focus on a number of poorly understood, if not totally unexplored, phenomena and effects which accompany doubly ionization and dramatically influence Auger decay rates and bandshape formation. Very relevant in this context is the analysis of the spatial distribution of the two electron vacancies in the system, and in particular the study of doubly hole localization effects, which can act to either enforce or destroy the atomic-like appearance of Auger spectra in molecular systems. Another aspect of the study concercs the effects of nuclear motion on the spectra, including vibrational effects and prototype cases of vibronic coupling. In this context, an approach based on the analysis of the moments of the cross-section distribution is discussed.
A subject of extreme importance towards the theoretical understanding of Auger spectroscopy analysis of general materials is the modelling of fundamental surface and solid state effects.
Institution: NIST, U.S.A.
Postal address: Bldg. 221, Rm. B-208, Gaithersburg, MD 20899 U.S.A.
Telephone: (US) 301 975-2349
Fax: (US) 301 975-2950
E-mail: eric.shirley@nist.gov
WWW home page: http://www.nist.gov/
Eric L. Shirley
National Institute of Standards and Technology
Bldg. 221, Rm. B-208
Gaithersburg, Maryland 20899
X-ray absorption spectra and resonant x-ray fluorescence spectra are modeled. In the latter, one considers emission of x-rays as given by a coherent absorption-emission process described by the classic Kramers-Heisenberg formula. Following x-ray absorption, an excited electrons is attracted by the ``core-hole'' created during absorption, and effects of this attraction can be modeled by solving the Bethe-Salpeter equation for the coupled, electron-core hole propagator. Many aspects of this core-hole-exciton problem are simple compared to the more familiar, valence-hole-exciton problem. However, with the desirability of addressing the latter in mind, many algorithmic developments which are applied and presented should benefit future work on the latter.
electron spectroscopy of solids
optical properties of solids
photonics and diffraction theory
Institution: Max-Planck-Institut für Physik komplexer Systeme,
Postal address: Nöthnitzer Straße 38, D-01187 Dresden,
Germany
E-mail: shukla@idefix.mpipks-dresden.mpg.de
Alok Shukla, Michael Dolg, Peter Fulde
Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Stra{\ss}e 38, D-01187 Dresden, Germany}
Hermann Stoll
Institut für Theoretische Chemie, Universit\"at Stuttgart, D-70550 Stuttgart, Germany
An ab initio Hartree-Fock approach aimed at directly obtaining the localized orthogonal orbitals (Wannier functions) of a crystalline insulator will be discussed. Results of its applications to perform all-electron calculations on the ground states of crystalline lithium hydride, lithium fluoride and lithium chloride without the use of any pseudo or model potentials will be presented. Quantities such as total energy, x-ray structure factors and Compton profiles obtained using the localized Hartree-Fock orbitals are shown to be in excellent agreement with the corresponding quantities calculated using the conventional Bloch-orbital based Hartree-Fock approach. The role of these Wannier functions in future correlated calculations on both the ground and the excited states will also be discussed.
Institution: Department of Chemical Physics and Material Science
Centre
Postal address: Rijksuniversiteit Groningen, Nijenborgh 4, 9747
AG Groningen, The Netherlands
Telephone: (31)-50-3634861 secr. (31)-50-3634440
Fax: (31)-50-3634441
E-mail: snijders@chem.rug.nl
WWW home page: none
J.G.Snijders
Department of Chemical Physics and Material Science Centre
Rijksuniversiteit Groningen
Nijenborgh 4
9747 AG Groningen
The Netherlands
Density Functional Theory (DFT) has proved very successful in the past twodecades or so in describing the static electronic structure of molecules ofconsiderable size, including such properties as bonding energies, potentialsurfaces, geometries, vibrational structure and charge distributions. Inits original form, however, DFT is essentially confined to groundstate properties and the response of this groundstate to static external perturbations such as electric fields. More recently the theory has beengeneralized to include the effects of time dependent perturbations (such asradiation fields) leading to Time Dependent Density Functional Theory(TDDFT) [1] which in form looks very similar to Time Dependent Hartree Fock(TDHF) also known as the Random Phase Approximation (RPA), but which ispotentially exact. The theory has been implemented [2,3] in the AmsterdamDensity Functional (ADF) programme package in its adiabatic form, where itis assumed that the time dependent density functional can be taken to beidentical to the static functional but where the static density is replacedby its time dependent counterpart. This adiabatic approximation has provento be quite accurate and has been applied by us to a wide variety of(mainly spectroscopic) dynamic linear response properties such as frequencydependent dipole [2] and quadrupole polarizabilities [5], Raman intensitiesand depolarization ratios [4], isotropic and anisotropic van der Waalscoefficients (C6, C7 and C8)[2,5]. More recently we have extended the scopeto the calculation of non-linear response properties that describe e.g.Electric Field Induced Second Harmonic Generation, Third Harmonic Generation, Electro-Optical Kerr effect etc.
In the case of the fullerene C60 [6] we have been able to obtain the mostaccurate determination of the third order response funtion (gamma) to date,obtaining good agreement with the most recent experiments. Earlier estimates varied by several orders of magnitude, both theoretically andexperimentally.
An extra bonus of TDDFT is that it enables us to calculate excitation energies and oscillator strengths [7] in a consistent way, thus freeing DFTfrom its groundstate limitations. Experience in this area is just buildingup, but the first results look very promising. Applications to atoms andsmall molecules will be presented.
References
1. E.K.U. Gross, J.F. Dobson and M. Petersilka, in Density Functional
Theory,
edited by R.F.Nalewajski, Springer Series "Topics in Current
Chemistry"
(Springer, Heidelberg, 1996)
2. S.J.A. van Gisbergen, J.G.Snijders, E.J.Baerends, J.Chem.Phys.
103 (1995) 9347-9354
3. S. van Gisbergen, V. Osinga, O. Gritsenko, R. van Leeuwen,
J.G. Snijders, E.J. Baerends, J.Chem.Phys. 105 (1996) 3142-3151
4. S. van Gisbergen, J.G. Snijders, E.J. Baerends, Chem. Phys.
Lett. 259 (1996) 599-604
5. V.P. Osinga, S.J.A. van Gisbergen, J.G. Snijders, E.J.Baerends,
J.Chem.Phys. 106 (1997) 5109-5122
6. S.J.A. van Gisbergen, J.G. Snijders, E.J. Baerends, Phys. Rev.
Lett. 78 (1997) 3097-3100
7. M.Cassida, in Recent Developments and Applications of Modern
Density Functional Theory, editor J.M.Seminarion (Elsevier, Amsterdam,
1996)
(Time dependent) Density functional theory, applications to linear
and
non-linear response functions, excitation energies and intermolecular
interactions. Application to periodic systems, including polymers
and
surfaces.
Relativistic effects.
Environmental effects, synthesis of Molecular dynamics and DFT.
Scattering between oriented molecules
Institution: Dept. of Theor. Phys., Lund University.
Postal address: Solvegat 14A, S-22362 Lund, Sweden.
Telephone: +46-46-2229069
Fax: +46-46-2224438
E-mail: barth@teorfys.lu.se
C.-O. Almbaldh, U. von Barth, and R. van Leeuwen
Dept. of Theor. Phys.
Lund University, Sweden.
The Galitskii-Migdal (GM) formula and the variational expression of Luttinger and Ward (LW) are two of many ways of obtaining the total energy of a many-electron system. Within conserving approximations, they lead to the same result. The self-consistent GW approximation (GWA) is such a conserving theory which recently was shown to give a total energy of the electron gas of almost the same accuracy as that of elaborate Monte-Carlo calculations. When the self-consistency requirement is relaxed and a non-interacting Green's fuction is used when evaluating the energy, the GM formula gives relatively bad results whereas the LW expression almost reproduces the full GWA result. This result demonstrates that the LW functional has a very shallow minimum giving us the possibility to obtain accurate total energies by rather simple means.
The LW functional being based on an underlying $\Phi$- derivable
theory becomes rather awkward to construct beyond the GW level.
We have therefore constructed a new functional $\Psi[G,W]$ having
the Green's function $G$ and the screened interaction $W$ as two
independent variables. As in a $\Phi$- derivable theory, the functional
derivative of $\Psi$ with respect to $G$ yields the self-energy
$\Sigma$ but the functional derivative of $\Psi$ with respect
to $W$ yields the irreducible polarizability $P$. Based on the
$\Psi$ functional we construct a new variational functional for
the total energy which, at a given level of approximation, can
be evaluated at arbitrary G and W. We have found that, at the
GW level, our new functional gives almost GWA-quality energies
of the gas when the functional is evaluated at a non-inteacting
$G$ and a $W$ based on a simple plasmon-pole model. We find it
quite remarkable that such a cumputationally simple approach can
produce total energies comparable to the Monte-Carlo results.
In addition, with the new $\Psi$ functional, the next level of
accuracy beyond the GWA is easily constructed.
Application of many-body perturbation theory to the calculation
of static (total energies, geometries) and dynamic (photoemission,
XPS, Auger spectra) properties of molecules, metals, and insulators.
Development and application of density-functional theory to the
ground-state properties of molecules and solids. Time-dependent
density-functional theory and its application to atoms
and molecules exposed to intense laser fields.
U. von Barth, Different Approximations within Density Functional Theory, their Advantages and Limitations, in Methods of electronic structure calculations, Proceedings from Trieste, August 1992, Word Scientific, London (1994).
M. Springer, P.S. Svendsen, and U. von Barth, A Straight-forward Gradient Approximation for the Exchange Energy of s-p Bonded Solids, Phys. Rev. B 54, 17392 (1996).
U. von Barth and B. Holm, Self-consistent GWo results for the electron gas: Fixed screened potential Wo within the random-phase approximation, Phys. Rev. B 54, 8411 (1996).
B. Holm and U. von Barth, Total energies from GW calculations, part of the thesis of B. Holm, February 28, 1997.
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